Manganese/oxygen compound with arsenic adsorption, arsenic adsorbent, and method of adsorptively removing from aqueous solution

ABSTRACT

A novel technique by which not only pentavalent arsenic but trivalent arsenic, which has been difficult to remove, can be efficiently removed. The manganese/oxygen compound which adsorbs arsenic is characterized by being a product of burning or heating which comprises an oxygen compound of bismuth and an oxygen compound of manganese and by containing manganese as a major component. It is used to treat an aqueous arsenic solution to thereby adsorptively remove the arsenic.

TECHNICAL FIELD

[0001] The invention of the present application relates to a manganeseoxygen compound with arsenic sorbability, arsenic adsorbent, and amethod of adsorption and removal of arsenic in solution.

BACKGROUND ART

[0002] Pollution of rivers and water area such as lakes and marshlandsby arsenic is prevailing in Japan and foreign countries, and examples inBangladesh have been widely reported. Soils in this country is abundantin arsenic, and skin failures and diseases by arsenic are often seen ininhabitants in the country using well water polluted with arsenic asdrinking water. While the concentration of arsenic is supposed to reach0.01 to 1 mg/liter (0.01 mg/liter according to the water qualitystandard by WHO) in Nawabganj district where the damage is reported tobe most serious in Bangladesh, no substantial countermeasures are takentoday. On the other hand, pollution by arsenic in Japan is mainly causedby waste water from abandoned mines. The concentration of arsenic in therivers around the mines ascribed to waste water from tunnels afterclosing the mines has been reported to be 0.08 to 1.3 mg/liter, whichexceeds the environmental standard, around Sasagatani Mine in ShimanePrefecture. In the surrounding area of former Horobetu Sulfur Mine inHokkaido, the concentration of arsenic in the liver had exceeded farabove the environmental standard before 1975 due to efflux of stronglyacidic water containing a large quantity of arsenic into Benkei River.On the other hand, it was reported that the original arsenicconcentration of 0.2 mg/liter had decreased to about {fraction (1/10 )}of 0.02 mg/liter since 1981 thanks to countermeasures to pollution bymining including blocking of entrance of tunnels and installation of aneutralization plant of mine water effected by Sobetsu Town. However,the total amount of use of lime cakes, slaked lime and calcium carbonateused for neutralization and removal of arsenic by coprecipitation inthis plant annually accounts for 40,000 to 50,000 tons, and it has beena large problem to ensure landfill sites of a vast amount ofprecipitates generated from the neutralization plant, and to cover theexpense of about 300 million yen per year. There are many waterpollution problems by arsenic such as those ascribed to waste water fromgeothermal power plants and industrial waste other than the problemsabove. However, since the currently prevailing coprecipitation methodinvolves the problems of waste disposal and treatment cost, treatmentsby arsenic adsorbents have been expected as substitutes of the arsenicprocessing method. Particularly, developments of novel adsorbents thatcan directly adsorb trivalent arsenic are considered to be valuable inestablishing an economically advantageous arsenic removal technique,because the process for oxidizing trivalent arsenic into pentavalentarsenic that is relatively easily adsorbed by adding an oxidizing agentmay be omitted.

[0003] The object of the present invention for solving the conventionaltechnical problems is to provide a novel technique that is able toefficiently remove, to say nothing of pentavalent arsenic, trivalentarsenic that has been considered to be difficult to remove.

DISCLOSURE OF INVENTION

[0004] In order to solve the above problem, firstly, the presentinvention provides a manganese oxygen compound with arsenic sorbabilitycharacterized by being a product of burning or heating which comprisesan oxygen compound of bismuth and an oxygen compound of manganese and bycontaining manganese as a major component.

[0005] Further, secondly, the present invention provides the manganeseoxygen compound with arsenic sorbability, characterized in that acompound of manganese in which a compound of bismuth is added is burnedor heated in the atmosphere or an atmosphere containing oxygen. Further,thirdly, the present invention provides a manganese oxygen compound witharsenic sorbability, characterized in that the product of burning orheating is an acid-treated product.

[0006] Preferably, fourthly, the present invention provides themanganese oxygen compound with arsenic sorbability, characterized inthat a mixture of oxidized bismuth carbonate powder, and manganesecarbonate powder is burned or heated at a temperature of 150° C. to 400°C. Fifthly, the present invention provides the manganese oxygen compoundwith arsenic sorbability, characterized in that a mixture of oxidizedbismuth carbonate and manganese carbonate is in the range of 0.05:1 to1:1.

[0007] Sixthly, the present invention provides an arsenic adsorbentcharacterized by comprising the oxygen compound of manganese accordingto any one of the above oxygen compounds of manganese, or a compoundcontaining these oxygen compounds of manganese. Seventhly, the presentinvention provides an arsenic adsorbent characterized by comprising themanganese oxygen compound retained on or filled in a carrier substance.

[0008] Further, eighthly, the present invention provides a method ofadsorption and removal of arsenic in solution which comprises,contacting an arsenic adsorbent and an aqueous arsenic solution, andadsorbing and removing arsenic contained in solution. Further, ninthly,the present invention provides a method of reclaiming the arsenicadsorbent which comprises, performing an acid treatment to an arsenicadsorbent which adsorbed arsenic by the above method, making arsenicdesorb into an acid solution, and enabling reclaim of the arsenicadsorbent.

[0009] As described above, the oxygen compound mainly containingmanganese according to the present invention can solve the problem oflow economical performance involved in conventional methods (except theadsorption method), while enabling trivalent arsenic, which has beentechnically difficult to efficiently remove by conventional adsorptionmethods, to be efficiently removed by adsorption in a quite short periodof time. For example, the amount of adsorption of trivalent arsenic perone gram reaches 50 mg by using the adsorbent of the present invention.The invention also enables the adsorbent after adsorption of arsenic tobe reclaimed by allowing the adsorbent to contact an acid solution suchas dilute sulfuric acid to readily recover adsorbed arsenic into theacid solution.

[0010] It is an important feature of the present invention that thepresent invention is effective not only to arsenous acid as a trivalentarsenic but also to arsenic acid as a pentavalent arsenic. Since arsenicis usually dissolved in industrial waste water as pentavalent arsenicacid in most cases, the facts that the present invention is effectivenot only to the trivalent arsenous acid but also to the pentavalentarsenic acid means that the present invention has a wide applicabilityin treating waste water containing arsenic.

[0011] The adsorbent of the present invention exhibits excellentperformance as described above while having an advantage that theconcentration of electrolytes of the aqueous solution as an object oftreatment is not required to be increased, which is also an advantage ofwater cleaning using an adsorbent. In other words, manganese and bismuthas the major components of the adsorbent are little dissolved in theaqueous arsenic solution as the object of treatment.

[0012] It has been a general method for retaining a powdery adsorbent tofill in a column after granulation using PVC and the like. However,since bonding surfaces with PVC are formed in the conventional method,the contact area between the adsorbent particles and treating solutionis reduced to consequently decrease the performance of the column.Accordingly, a novel technique for retaining the powdery adsorbent usingfibrous carrier substances such as ashless pulp or glass wool has beendeveloped in the present invention to improve the drawbacks of theconventional method.

BRIEF DESCRIPTION OF DRAWINGS

[0013]FIG. 1 is a graph showing the relation between the mixing weightratio of manganese carbonate and oxidized bismuth carbonate, and theamount of adsorption of arsenic.

[0014]FIG. 2 is a graph showing the relation between the burningtemperature and the amount of adsorption of arsenic.

[0015]FIG. 3 is a graph showing the relation after correction of therelation in FIG. 2.

[0016]FIG. 4 is a graph showing the relation between initial pH and theamount of adsorption of arsenic.

[0017]FIG. 5 is a graph showing the relation between the desorptionratio and adsorption time.

[0018]FIG. 6 is a graph showing the relation between the concentrationof arsenic in aqueous solution and the amount of adsorption of arsenic.

[0019]FIG. 7 is a graph showing the relation between the stirring timeand the concentration of arsenic.

[0020]FIG. 8 illustrates an example of waste water treatment using anadsorption column.

[0021]FIG. 9 is a graph showing the result of arsenic waste watertreatment by the adsorption column method.

[0022]FIG. 10 illustrates an example of a simplified water cleaningmethod using an adsorption mat.

[0023]FIG. 11 illustrates an example of a portable water cleaning methodusing an adsorption pack.

[0024]FIG. 12 is a graph showing the result of waste water treatment byan adsorption pack method.

[0025]FIG. 13 is a graph showing the result of treatment of pentavalentarsenic containing waste water.

BEST MODE FOR CARRYING OUT THE INVENTION

[0026] While the invention is featured as described above, embodimentsthereof will be described hereinafter.

[0027] The oxide compound of manganese provided by the invention has anarsenic sorbability as its function. The compound contains an oxygencompound of bismuth (Bi) and an oxygen compound of manganese (Mn) withmanganese as its major component.

[0028] This product of burning or heating refers to as a heated product,and means that the product is heated either by the heat of a chemicalreaction induced by mixing base materials, by drying, or by a heattreatment accompanied by a chemical reaction. Burning, or heating isusually carried out at 100° C. or more, preferably in the temperaturerange of 150 to 500° C., and the oxygen compound of bismuth and theoxygen compound of manganese are involved by heating. The “oxygencompound” is, as well, defined as an oxide or an oxide as a complexoxygen compound, or a compound mainly comprising the oxygen compound andhaving oxygen containing groups such as carboxylate groups.

[0029] Various bismuth compounds and manganese compounds may be used asthe base materials for forming the oxygen compound in the atmosphere oran atmosphere containing oxygen in burning or heating. The base materialmay be carboxylate, nitride, sulfate, organic acid salts and halides,and favorably used compounds are solids or powders. The material may beformed by precipitation by a sol-gel method.

[0030] In a representative example, oxidized bismuth carbonate powderand manganese carbonate powder are mixed, and the mixed powder or amolded body thereof is burned in the temperature range of 150 to 400°C., preferably 170 to 250° C. The mixing ratio of the base materialssuch as oxidized bismuth carbonate and manganese carbonate in therepresentative example is preferably 0.01:1 to 1:1 in the molar ratio ofbismuth to manganese considering the arsenic adsorbing ability.

[0031] It is effective to activate the burned product by an acidtreatment for preparing the arsenic adsorbent. Dilute nitric acid,sulfuric acid, hydrochloric acid and the like may be used for the acidtreatment.

[0032] The arsenic adsorbent of the present invention may be retained onor filled in a carrier substance such as ashless pulp and glass wool foruse in removal of arsenic in aqueous solution by adsorption.

[0033] Trivalent arsenic has been treated after converting it intoreadily treatable pentavalent arsenic by adding an oxidizing agent inthe conventional art. However, it is a problem that water quality isdeteriorated by increasing the electrolyte concentration in water whilebeing low in cost performance. Accordingly, developments of adsorbentscapable of directly treating trivalent arsenic in water have beendesired. The present invention can realize a high performance,economically advantageous adsorption treatment of trivalent arsenic aswell as pentavalent arsenic by the steps comprising burning themanganese compound by adding a small amount of a bismuth compound, andapplying the obtained metal oxide containing manganese as a majorcomponent with a small amount of bismuth to waste water containingarsenic, desirably after an acid treatment. Adsorption of trivalentarsenic has been experimentally proved as arsenic in arsenous acid(HAsO₂) by measuring pH and redox potential of the aqueous arsenicsolution.

[0034] A retention layer of the powdery adsorbent excellent in chemicalresistance in repeated uses of the column may be obtained by using glasswool and the like as the carrier of the adsorbent. Incineration fordisposal of the column in an incinerator after repeated uses of thecolumn is possible by using ashless pulp as the carrier of theadsorbent. The ashless pulp accounting for the greater part of thevolume of the retaining layer involving the powdery adsorbent is almostcompletely burnt up, and the residue only comprises the component of theadsorbent after incineration.

[0035] Accordingly, the present invention provides a novel adsorbentcapable of efficiently adsorbing, to say nothing of pentavalent arsenic,trivalent arsenic that has been considered to be difficult to removefrom an aqueous solution by the conventional art. The adsorbent has ahigh performance in which the maximum amount of arsenic per 1 g of theadsorbent reaches 50 mg or more.

[0036] The following procedure give a largest effect in applying theadsorbent of the invention to an aqueous arsenic solution. This will bemade apparent in the examples to be described hereinafter.

[0037] (a) Manganese carbonate powder (MnCO₃, reagent special grade) andoxidized bismuth carbonate powder (Bi₂(CO₃)O₂, reagent special grade)are mixed in a weight ratio of 1:0.1 to 1:0.2. A metal oxide containingbismuth and mainly containing manganese is synthesized by burning themixture at 200° C. for 4 hours and 30 minutes using an electric furnace.

[0038] (b) The metal oxide containing bismuth and mainly containingmanganese obtained in (a) is suspended in dilute nitric acid with aconcentration of about 0.5 mol/liter to remove remaining carbonatecomponents by vaporization. Then, the metal oxide is washed with purewater to remove adhered nitric acid.

[0039] (c) The sample obtained in (b) is dried at about 100° C. for 1hour using a drying machine. The adsorbent is produced by the procedureabove.

[0040] (d) The adsorbent is suspended in dilute nitric acid with aconcentration of about 0.5 mol/liter followed by stirring for 30 minutesto 1 hour, filtered, washed with pure water, and suspended again in anaqueous arsenic solution for use as the adsorbent.

[0041] (e) After the concentration of arsenic in the aqueous arsenicsolution has decreased to 0.1 mg/liter as a standard of waste water, theadsorbent is retrieved from the aqueous arsenic solution by, forexample, filtration. Purified waste water becomes possible to dischargeinto a public water area.

[0042] (f) Adsorbed arsenic is desorbed and concentrated in dilutesulfuric acid by adding a small volume of dilute sulfuric acid with aconcentration of 0.5 mol/liter or less to the adsorbent after adsorbingretrieved arsenic, followed by stirring for about 30 minutes.

[0043] (g) Since adsorption ability of the adsorbent after desorption ofarsenic is recovered again, the adsorbent is used again by allowing itto contact the aqueous arsenic solution.

[0044] While the adsorbent is suspended in the aqueous arsenic solutionas a powdery adsorbent in the example above, the adsorbent may begranulated or retained on a porous carrier, if necessary, to fill in acolumn for industrial applications in order to remove arsenic by passingthe aqueous arsenic solution through the column.

[0045] While the invention will be described in more detail withreference to the examples, the invention is by no means restricted tothe examples.

EXAMPLES Example 1

[0046] Synthesis of Adsorbent and Adsorption of Arsenic

[0047] (Synthesis of Adsorbent)

[0048] Manganese carbonate powder (MnCO₃, reagent special grade) andoxidized bismuth carbonate powder (Bi₂(CO₃)O₂, reagent special grade)were thoroughly mixed by changing the mixing ratios to several steps.About 20 g of each mixed powder was transferred to a ceramic crucible,and was burned at 400° C. for 4.5 hours using an electric furnace,followed by cooling to room temperature by allowing the crucible tostand still. The metal oxide obtained containing a small amount ofbismuth and manganese as a major component after burning is used as anadsorbent for the arsenic adsorption experiment. The optimum mixingweight ratio between manganese carbonate (MnCO₃) powder and oxidizedbismuth carbonate (Bi₂(CO₃)O₂) powder was determined for obtaining thehighest amount of adsorption. The effect of adding bismuth was confirmedby comparing the adsorptive performance of manganese oxide, which wasobtained by burning only manganese carbonate (MnCO₃) powder withoutmixing with oxidized bismuth carbonate (Bi₂(CO₃)O₂) powder, with theadsorptive performance of the adsorbent above.

[0049] Then, the sample was heated or burned by changing thetemperatures to 150° C., 200° C., 250° C. and 300° C. for 4.5 hoursfollowed by allowing the samples to cool to room temperature. Theoptimum burning temperature was investigated by arsenic adsorptionexperiments using each metal oxide obtained containing a small amount ofbismuth and mainly containing manganese as the adsorbent.

[0050] (Experimental Method of Arsenic Adsorption)

[0051] An aqueous arsenic standard solution (made by Wako Pure ChemicalIndustries, Ltd.) containing a total concentration of trivalent arsenicof 1000 mg/liter prepared from a reagent (As₂O₃) was diluted withion-exchange water to prepare 1000 ml each of arsenic solutions withconcentrations of 10 mg/liter, 20 mg/liter or 40 mg/liter, and thesolution was used for each experiment. The pH values of the arsenicsolutions were adjusted using an aqueous sodium hydroxide solution.Subsequently, 1.0 g of the adsorbent obtained by each experiment abovewas weighed with an electronic balance, and was suspended in 1000 ml of0.5 mol/liter of diluted nitric acid (may be diluted sulfuric acid orhydrochloric acid) followed by stirring for 1 hour. After stirring, thesuspension was filtered with suction using a glass fiber filtrationpaper (GS25, made by Toyo Roshi Kaisha, Ltd.) with a pore size of 0.6mm, followed by washing by allowing 1000 ml of ion-exchange water toflow through (this process is called as an acid treatment hereinafter)The activated adsorbent obtained by the acid treatment was suspended inan arsenic aqueous solution followed by stirring for 1 hour. Twentymilliliters each of the aqueous arsenic solutions were sampled at 5, 10,20, 30 and 60 minutes after the start of stirring. A disposable membranefilter (DISMIC-25 made by Toyo Roshi Kaisha, Ltd.) with a pore size of0.2 μm was used for filtration. The concentration of arsenic in eachfiltered sample was measured with an ICP atomic emission analyzer(ICPS-1000III made by Shimadzu Corporation) to obtain time dependentchanges of the arsenic concentration in the aqueous arsenic solution.

[0052] (Amount of Adsorption of Arsenic and Mixing Ratio of BaseMaterial)

[0053] For synthesizing the arsenic adsorbent, the mixing ratio ofmanganese carbonate powder (MnCO₃, reagent special grade) and oxidizedbismuth carbonate powder (Bi₂(CO₃)O₂, reagent special grade) werechanged as described above to investigate the optimum mixing ratio. Theburning temperature was 400° C., and the results are shown in FIG. 1.FIG. 1 shows that the optimum mixing ratio for obtaining the highestamount of adsorption is MnCO₃ :Bi₂(CO₃)O₂ of about 1:0.1 to 1:0.2 in themixing weight ratio. On the contrary, the amount of adsorption wasextremely decreased in the manganese oxide containing no bismuth added(mixing ratio 1:0) as compared with the oxide in which bismuth is added,indicating that the arsenic adsorption performance is improved by addingbismuth.

[0054] Peaks of bismuth oxide and oxidized bismuth carbonate, as well asa broad peak at 2θof 37° a scribed to amorphous manganese oxide, wereobserved by confirmation with the X-ray diffraction pattern in theproducts of burning with the mixing ratio in the range of 1:0.1 to1:0.2.

[0055] (Amount of Adsorption of Arsenic and Burning or HeatingTemperature)

[0056] In the synthesis of the arsenic adsorbent, the change of theamount of adsorbed arsenic to the difference of the temperature wasinvestigated when a mixed powder of manganese carbonate and oxidizedbismuth carbonate was heated using an electrical furnace. The resultsare shown in FIG. 2. FIG. 2 shows that a high amount of adsorption isobtained when the temperature is about 300° C. However, it was foundthat the weight of the adsorbent was decreased to about one half of theinitial weight of 1 g, when the adsorbent suspended in an aqueousarsenic solution was filtered and weighed after completing theadsorption procedure. This decrease of the weight of the adsorbent issupposed to be ascribed to the fact that manganese carbonate as a basereagent material is left behind in the adsorbent obtained after burningor heating, and carbonates are lost by vaporization when the adsorbentis treated with an acid. It was made clear that the adsorbent obtainedby burning or heating at 200° C. shows the highest amount of adsorptionas shown in FIG. 3, by correcting the results in FIG. 2 considering theweight loss as described above.

[0057] (Amount of Adsorption of Arsenic and pH)

[0058] The effect of pH of the aqueous solution of the removal object onthe amount of adsorption of arsenic was investigated. The result showedthat good adsorption of arsenic is attained when pH of the aqueousarsenic solution is weakly acidic. Accordingly, arsenic is considered tobe efficiently removed by previously adjusting pH of the aqueous arsenicsolution as the object of removal.

[0059] (Desorption of Arsenic from the Adsorbent)

[0060] Arsenic adsorbed on the adsorbent is efficiently desorbed byallowing the adsorbent to contact an acid such as dilute sulfuric acid.The relation between the kind of the acid solution used for desorptionand desorption ratio is shown in FIG. 5. FIG. 5 shows that a high degreeof desorption is possible by using dilute hydrochloric acid or dilutesulfuric acid.

[0061] (Concentration of Arsenic in Aqueous Solution and Amount ofAdsorption of Arsenic)

[0062] The effect of the concentration of arsenic in the aqueoussolution on the amount of adsorption is shown in FIG. 6. FIG. 6 showsthat the amount of adsorption increases as the concentration of arsenicis increased.

[0063] (Practical Application to Aqueous Waste Arsenic Solution)

[0064] Effectiveness of the synthesized adsorbent to practical aqueouswaste arsenic solution containing trivalent arsenic was confirmed. Theobject of treatment was waste water from a currently operatinggeothermal power plant. This waste water contains arsenic in aconcentration of 3.5 mg/liter. The component and pH of this waste waterare shown in Table 1. Table. 1 shows that this waste water contains manycomponents other than arsenic. In an actual experiment, 1 g of theadsorbent having the mixing ratio of 1:0.2 as described above and burnedat 200° C. was treated with an aqueous nitric acid with a concentrationof 0.5 mol/liter, and the adsorbent was suspended in 1 liter of wastewater with stirring for 1 hour. The results are shown in FIG. 7. FIG. 7shows that the concentration of arsenic in the waste water was decreasedto 0.1 mg/liter or less that is the standard of waste water in a periodof as short as 5 minutes from the initial concentration of 3.5 mg/liter.This results shown that the adsorbent of the invention is quiteeffective for the practical arsenic waste water. TABLE 1 Components ofpractical waste water and pH Chemical Concentration Element (mg/l) Na1790 K 257 Ca 28.0 Mg 0.70 Cl 2980 SO₄ 144 HCO₃ 23.9 Fe 4.5 HBO₃ 159 As3.50 T-SiO₂ 667 Li 10.8 pH 7.0

Example 2

[0065] [Retention and Adsorption of Powdery Adsorbent using Ashless Pulpand Glass Wool]

[0066] The adsorbent is granulated or retained on a porous carrier tofill in a column, if necessary, for industrial applications, and arsenicis removed by allowing an aqueous arsenic solution to flow through thecolumn.

[0067] (1) Method for retaining powdery adsorbent.

[0068] An appropriate amount of ashless pulp or glass wool with athickness of about 1 μm was added in pure water with thorough stirring.The diameter of the ashless pulp or glass wool depends on the size ofthe adsorbent particles to be retained. For example, the diameter of theadsorbent particles as the retention object is 1 to several tensmicrons. Then, the adsorbent is added to the suspension of ashless pulpor glass wool with additional stirring. An inorganic acid such ashydrochloric acid or nitric acid is added when necessary depending onthe property of the adhesive with stirring for a predetermined time.Adding the inorganic acid with stirring activates the surface of theadsorbent particles.

[0069] The suspension is added in small portions from the top of acylinder for preparing an adsorption column when glass wool is used, andthe liquid is completely discharged from the bottom of the column withsuction using a pump every time for adding the suspension. Thisprocedure is repeated until a desired thickness is obtained to form aretention layer in which the powdery adsorbent is embedded in the glasswool fiber.

[0070] When ashless pulp is used, on the other hand, the suspension ispoured into the cylinder for preparing an adsorption column from the topof the column. The suspension is stirred with a bar so that the pulp andadsorbent are uniformly precipitated in the column while allowing theliquid to be gradually discharged from the bottom of the column, and aretention layer is formed so that the powdery adsorbent is embedded inthe ashless pulp fibers.

[0071] (2) Examples Depending on the Retention Method

[0072] Examples of treatments of water containing arsenic by applyingthe retention methods of the invention described above are explainedbelow.

[0073] (a) Adsorption Column Method

[0074] In this method, wastewater containing trivalent arsenicdischarged from semiconductor factories is the object of treatment. Asshown in FIG. 8, arsenic is removed by injecting wastewater withcompression into the column from an waste water tank using a pump. Alarge volume of wastewater may be continuously processed by this method.A valve is provided between the pump and adsorption column to controlthe feed rate to the adsorption column. The adsorption column ishermetically sealed to prevent the arsenic adsorbent from contacting theair in order to protect the adsorptive performance of the adsorptioncolumn from being deteriorated due to drying of the adsorbent. FIG. 9shows the experimental results of arsenic wastewater by this method. Theresults were obtained from experiments by flowing an aqueous arsenicsolution with an arsenic concentration of 1 ppm through a cylindricaladsorption column with a diameter of 2 cm and a length of 10 cm at aflow speed of 300 ml/h.

[0075] (b) Adsorption Mat Method

[0076] This method has been devised as an water cleaning technology fortreating serious contamination of drinking water with arsenic occurringin Bangladesh, which is expected as a simple water cleaning method thatdoes not require any electricity at all. The treatment tank shown inFIG. 10 comprises an outer frame equipped with an water tap, an arsenicadsorption mat, and charcoal, sand and gravel that has been used fordomestic filtration tank. This device is featured in that the structureis simple and hardly broken, and cleaning of water from arsenic ispossible by only supplying the outer frame and adsorption mat to theinstallation site. The gravel layer and sand layer remove suspended fineparticles in water, the charcoal layer removes organic substances, andthe adsorption mat to enable safe drinking water to be easily obtainedremoves arsenic. In addition, the structural feature of the method isthat the elevation of the water tap is made to be higher than theinstallation position of the arsenic adsorption mat so that theadsorption mat is always soaked in water. This enables the adsorbent tobe protected from being dried by contacting the air to consequentlyprevent the performance of the adsorption mat from being deteriorated.

[0077] An arsenic adsorbent previously activated with an inorganic acidis retained on the adsorption mat. The adsorption mat should behermetically sealed to the air in a sufficiently moist state, and isstored separately from the outer frame. The adsorption mat istransported to the installation site of the device in a hermeticallysealed state with a film. The film is peeled immediately before use andis laid in the outer frame, and sand, gravel and charcoal are filledthereon as shown in the drawing.

[0078] c) Adsorption Bag Method

[0079] This method was devised as a portable cleaning method of waterfrom arsenic for the purpose of enhancing simplicity and convenience ascompared with the method (b) . The method is illustrated in FIG. 11. Asmall amount of glass wool for obtaining good water permeability orfiber of ashless pulp or the like, and the arsenic adsorbent are sealedin an adsorption bag. The bag is placed in water to be treated, andarsenic is removed by adsorption by stirring water to be treated.

[0080] The arsenic adsorbent in the adsorption bag is previouslyactivated with an inorganic acid, and the bag is hermetically sealed ina plastic bag in a moist state. The adsorptive ability of the arsenicadsorbent is sustained for a long period of time by hermetic sealing.Taking the adsorption bag out of the plastic bag by breaking the plasticbag may instantaneously use the adsorbent. FIG. 12 shows the results ofuse of this method. FIG. 12 shows the decrease of the concentration ofarsenic after placing one adsorption bag with stirring in 1 liter ofwater containing trivalent arsenic.

Example 3

[0081] [Removal of Arsenic (Pentavalent Arsenic) from IndustrialWastewater]

[0082] (Experimental Wastewater)

[0083] Arsenic (V) was removed from practical industrial waste waterhaving the compositions shown in Table 2 using an adsorbent having amixing weight ratio of 1:0.2 as described previously and burned at 200°C. The arsenic concentration of waste water was 0.028 mg/liter, whichexceeds the environmental standard of 0.01 mg/liter. Arsenic in thiswastewater was confirmed to be arsenic acid from the measurement of theredox potential. TABLE 2 concentration component (mg/l) As 0.028 Mo 310V 2.5 Pb 0.3 Cd 0.1 Cr 0.1 Se 0.3 Mn 3.4 Zn 0.1 Cu 0.1 P 1.0 Fe 0.1 Al1.3 NH₄—N 1980 NO₃—N 850 Na 3720 Mg 6800 Ca 140 S 9495 Cl 6750 pH 7.8

[0084] (Experimental Conditions)

[0085] The adsorbent (1.44 g) after an acid treatment with 0.5N nitricacid was suspended in 1 liter of experimental waste water. Samples ofexperimental waste water were sampled by filtration at every time lapseof 5, 15, 30, 60 and 120 minutes after suspending the adsorbent. Thechanges of arsenide concentration in experimental waste water wereinvestigated using an ICP atomic emission analyzer equipped with ahydride compound generator, which is a higher analytical sensitivitythan conventional ICP atomic emission analyzer.

[0086] (Experimental Results)

[0087] As shown in FIG. 13, the concentration of arsenic was decreasedwith the time lapse of stirring as indicated in the vertical axis, andreached to a level below the environmental standard of 0.01 mg/liter 30minutes after suspending the adsorbent. It was confirmed that theadsorbent of the invention is also effective for removing arsenic (V) inpractical industrial waste water in which various other components existtogether as shown in Table 2.

Example 4

[0088] [Removal of Arsenic from Artificial Arsenic (V) Waste Water]

[0089] (Experimental Waste Water)

[0090] Artificial waste water (3 liters) of arsenic (V) was prepared bydissolving a reagent (Na₂HAsO₄) in pure water. The concentration ofarsenic was 10 mg/liter, and the solution was adjusted to pH 7 by addingan aqueous sodium hydroxide solution.

[0091] (Experimental Conditions)

[0092] After treating 1 g of the adsorbent in Example 3 with 0.5N nitricacid for 30 minutes, the adsorbent was washed with pure water, andsuspended in experimental waste water with stirring for 1 hour.

[0093] (Experimental Results)

[0094] The concentration of arsenic in experimental waste water after atime lapse of 1 hour was determined with an ICP atomic emissionanalyzer, and was found to be decreased to7.2 mg/liter. The weight ofthe adsorbent recovered from experimental waste water by filtration was0.5 g. The amount of adsorption of arsenic (V) per unit weight of theadsorbent was calculated to be 16.8 mg/g. The value was almostcomparable to the experimental result obtained by using an artificialarsenic waste water containing arsenic (III) prepared using a reagentAs₂O₃, showing that the adsorbent of the invention is an effectiveadsorbent for trivalent arsenic as well as for pentavalent arsenic.

[0095] Industrial Applicability

[0096] As hitherto described in detail, the present invention provides anew technology that enables pentavalent arsenic as well as trivalentarsenic that has been considered to be difficult to remove to beefficiently removed from waste water.

1. An manganese oxygen compound with arsenic sorbability characterizedby being a product of burning or heating which comprises an oxygencompound of bismuth and an oxygen compound of manganese and bycontaining manganese as a major component.
 2. The manganese oxygencompound with arsenic sorbability according to claim 1, characterized inthat a compound of manganese in which a compound of bismuth is added isburned or heated in the atmosphere or an atmosphere containing oxygen.3. The manganese oxygen compound with arsenic sorbability, characterizedin that the product of burning or heating according to claim 1 or 2 isan acid-treated product.
 4. The manganese oxygen compound with arsenicsorbability according to any one of claims 1 to 3, characterized in thata mixture of oxidized bismuth carbonate powder and manganese carbonatepowder is burned or heated at a temperature of 150° C. to 400° C.
 5. Themanganese oxygen compound with arsenic sorbability according to any oneof claims 1 to 4, characterized in that the molar mixing ratio of thecompound of bismuth and the compound of manganese is in the range of0.01:1 to 1:1.
 6. An arsenic adsorbent characterized by comprising theoxygen compound of manganese according to any one of claims 1 to 5, or acompound containing these oxygen compounds of manganese.
 7. An arsenicadsorbent characterized by comprising the manganese oxygen compoundretained on or filled in a carrier substance.
 8. A method of adsorptionand removal of arsenic in solution which comprises, contacting anarsenic adsorbent according to claim 6 or 7 and an aqueous arsenicsolution, and adsorbing and removing arsenic contained in solution.
 9. Amethod of reclaiming the arsenic adsorbent which comprises, performingan acid treatment to an arsenic adsorbent which adsorbed arsenic by amethod according to claim 8, making arsenic desorb into an acidsolution, and enabling reclaim of the arsenic adsorbent.